The present invention relates generally to the field of electrosurgery, and more particularly to surgical devices and methods which employ high frequency electrical energy to treat tissue in regions of the spine. The present invention is particularly suited for the treatment of fissures in discs.
The major causes of persistent, often disabling, back pain are disruption of the disc annulus, chronic inflammation of the disc (e.g., herniation), or relative instability of the vertebral bodies surrounding a given disc, such as the instability that often occurs due to a degenerative disease. Spinal discs mainly function to cushion and tether the vertebrae, providing flexibility and stability to the patient""s spine. Spinal discs comprise a central hydrostatic cushion, the nucleus pulposus, surrounded by a multi-layered ligament, the annulus fibrosis. As discs degenerate, they lose their water content and height which brings the vertebrae closer together. This results in a weakening of the shock absorption properties of the disc and a narrowing of the nerve openings in the sides of the spine which may pinch the nerve. This disc degeneration can eventually cause back and leg pain. Weakness in the annulus from degenerative discs or disc injury can allow fragments of nucleus pulposus from within the disc space to migrate into the spinal canal. There, displaced nucleus or protrusion of annulus fibrosis, e.g., herniation, may impinge on spinal nerves. The mere proximity of the nucleus pulposus or a damaged annulus to a nerve can cause direct pressure against the nerve, resulting in numbness and weakness of leg muscles.
Often, inflammation from disc herniation can be treated successfully by non-surgical means, such as rest, therapeutic exercise, oral anti-inflammatory medications or epidural injection of corticosteroids. In some cases, the disc tissue is irreparably damaged, thereby necessitating removal of a portion of the disc or the entire disc to eliminate the source of inflammation and pressure. In more severe cases, the adjacent vertebral bodies must be stabilized following excision of the disc material to avoid recurrence of the disabling back pain. One approach to stabilizing the vertebrae, termed spinal fusion, is to insert an interbody graft or implant into the space vacated by the degenerative disc. In this procedure, a small amount of bone may be grafted from other portions of the body, such as the hip, and packed into the implants. This allows the bone to grow through and around the implant, fusing the vertebral bodies and alleviating the pain.
Until recently, spinal discectomy and fusion procedures resulted in major operations and traumatic dissection of muscle and bone removal or bone fusion. To overcome the disadvantages of traditional traumatic spine surgery, minimally invasive spine surgery was developed. In endoscopic spinal procedures, the spinal canal is not violated and therefore epidural bleeding with ensuring scarring is minimized or completely avoided. In addition, the risk of instability from ligament and bone removal is generally lower in endoscopic procedures than with open discectomy. Further, more rapid rehabilitation facilitates faster recovery and return to work.
Minimally invasive techniques for the treatment of spinal diseases or disorders include chemonucleolysis, laser techniques and mechanical techniques. These procedures generally require the surgeon to form a passage or operating corridor from the external surface of the patient to the spinal disc(s) for passage of surgical instruments, implants and the like. Typically, the formation of this operating corridor requires the removal of soft tissue, muscle or other types of tissue depending on the procedure (i.e., laparascopic, thoracoscopic, arthroscopic, back, etc.). This tissue is usually removed with mechanical instruments, such as pituitary rongeurs, curettes, graspers, cutters, drills, microdebriders and the like. Unfortunately, these mechanical instruments greatly lengthen and increase the complexity of the procedure. In addition, these instruments sever blood vessels within this tissue, usually causing profuse bleeding that obstructs the surgeon""s view of the target site.
Once the operating corridor is established, the nerve root is retracted and a portion or all of the disc is removed with mechanical instruments, such as a pituitary rongeur. In addition to the above problems with mechanical instruments, there are serious concerns because these instruments are not precise, and it is often difficult, during the procedure, to differentiate between the target disc tissue, and other structures within the spine, such as bone, cartilage, ligaments, nerves and non-target tissue. Thus, the surgeon must be extremely careful to minimize damage to the cartilage and bone within the spine, and to avoid damaging nerves, such as the spinal nerves and the dura mater surrounding the spinal cord.
Lasers were initially considered ideal for spine surgery because lasers ablate or vaporize tissue with heat, which also acts to cauterize and seal the small blood vessels in the tissue. Unfortunately, lasers are both expensive and somewhat tedious to use in these procedures. Another disadvantage with lasers is the difficulty in judging the depth of tissue ablation. Since the surgeon generally points and shoots the laser without contacting the tissue, he or she does not receive any tactile feedback to judge how deeply the laser is cutting. Because healthy tissue, bones, ligaments and spinal nerves often lie within close proximity of the spinal disc, it is essential to maintain a minimum depth of tissue damage, which cannot always be ensured with a laser. Monopolar radiofrequency devices have been used in limited roles in spine surgery, such as to cauterize severed vessels to improve visualization. These monopolar devices, however, suffer from the disadvantage that the electric current will flow through undefined paths in the patient""s body, thereby increasing the risk of unwanted electrical stimulation to portions of the patient""s body. In addition, since the defined path through the patient""s body has a relatively high impedance (because of the large distance or resistivity of the patient""s body), large voltage differences must typically be applied between the return and active electrodes in order to generate a current suitable for ablation or cutting of the target tissue. This current, however, may inadvertently flow along body paths having less impedance than the defined electrical path, which will substantially increase the current flowing through these paths, possibly causing damage to or destroying surrounding tissue or neighboring peripheral nerves.
The present invention provides systems, apparatus and methods for selectively applying electrical energy to structures within a patient""s body, such as tissue within or around the spine. The systems and methods of the present invention are particularly useful for ablation, resection, aspiration, collagen shrinkage, tissue bonding and/or hemostasis of tissue and other body structures in open and endoscopic spine surgery.
In one aspect of the invention, a method is provided for treating and sealing invertebrate discs which have tears or fissures on the annulus fibrosus. Specifically, the method of the present invention comprises introducing an electrosurgical probe to the outer surface of an annulus in close proximity to or in contact with a fissure in the annulus. High frequency voltage can then be applied between one or more active electrode(s) and one or more return electrode(s) to apply sufficient energy to the disc tissue to substantially seal the fissure on the annulus. The high frequency voltage will be directed only to the tissue immediately surrounding the fissure so as to reduce collateral heating and damage to the annulus tissue and nucleus pulposus.
In a specific configuration, electrically conducting fluid, such as isotonic saline, is directed to the target site, preferably between the fissure and the active electrode. In monopolar embodiments, the conductive fluid will typically be delivered such that the fluid substantially surrounds the active electrode, and provides a layer of fluid between the active electrode and the tissue. In bipolar embodiments, the conductive fluid preferably generates a current flow path between the active electrode(s) and one or more return electrode(s). The current flow path may be generated by directing an electrically conducting fluid along a fluid path past the return electrode and to the fissure, or by locating a viscous electrically conducting fluid, such as a gel, at the fissure, and submersing the active electrode(s) and the return electrode(s) within the conductive gel.
The fissure may be heated either by passing the electric current through the tissue to a selected depth before the current returns to the return electrode(s) and/or by heating the electrically conducting fluid in contact with the fissure. In the latter embodiment, the electric current may not pass into the tissue surrounding the fissure at all. In both embodiments, the heated fluid and/or the electric current elevates the temperature of the annulus tissue surrounding the fissure sufficiently to cause sealing of the fissure. The high frequency voltage is applied to the active electrode(s) to elevate the temperature of tissue immediately surrounding the fissure from body temperature (about 37xc2x0 C.) to a tissue temperature in the range of about 45xc2x0 C. to 90xc2x0 C., usually about 60xc2x0 C. to 70xc2x0 C., to seal the fissure.
In another aspect, the present invention provides a method of treating a fissure. A sealant or bonding material, such as a fibrogen glue or collagen, is delivered to the fissure. The sealant can be heated so as to seal the fissure.
In a specific configuration, the sealant is directed through a tube or a catheter and onto the fissure. The tube can be disposed within the probe or a separate instrument. An opening or a plurality of openings can be disposed near the distal end of the tube or along the lumen of the tube to deliver the sealant from the tube to the fissure. After the sealant has been delivered to the fissure, high frequency energy, such as RF, can be delivered to heat the sealant to a specified temperature to harden and cover the fissure. Preferably, the high frequency energy can be applied in a sufficient amount to effectively cause the sealant to harden while avoiding damage to the surrounding tissue.
In another aspect, the present invention provides an electrosurgical apparatus for treating a fissure in the annulus. The apparatus comprises an elongate shaft having a proximal end portion and a distal end portion. An active electrode is disposed on the distal end portion of the shaft. The apparatus further comprises a return electrode and a high frequency voltage source which can generate a voltage sufficient to seal the fissure.
The probe will typically have a suitable diameter and length to allow the surgeon to reach the fissure by delivering the shaft through a percutaneous penetration in the thoracic cavity, the abdomen, the back, or the like. The shaft of the probe may be rigid or flexible. In most embodiments, however, the shaft of the probe is semi-flexible or catheter like so as to permit the treating physician to direct the electrode from a proximal end of the shaft to the target disc. Alternatively, in any of the embodiments, the probe may be introduced through a percutaneous penetration in the body and to the target disc through a rigid external tube or a trocar cannula. A trephine or other conventional instrument may be used to form a channel from the trocar cannula through the annulus fibrosus and into the nucleus pulposus.
The probe of the present invention may use a single active electrode or an electrode array distributed over a contact surface of a probe. The electrode array usually includes a plurality of independently current-limited and/or power-controlled active electrodes to apply electrical energy selectively to the target tissue while limiting the unwanted application of electrical energy to the surrounding tissue and environment resulting from power dissipation into surrounding electrically conductive liquids, such as blood, normal saline, electrically conductive gel and the like.
In a specific configuration the active electrodes are disposed in a linear arrangement near or at the distal end of the probe so as to define an edge which can promote localized electric fields between the edge and the fissure. The use of the linear electrodes increase the electric field intensity and reduce the extent or depth of tissue heating as a consequence of the divergence of current flux lines which emanate from the exposed surface of each active electrode. The linear electrodes provide an interface which can engage an approximately linear fissure and focus the electrical energy directly to the tissue within the fissure. As a result, the linear arrangement can improve the sealing of the fissure and reduce the collateral damage to the surrounding tissue.
In an exemplary embodiment of the apparatus, the return electrode is disposed on the shaft and spaced apart from the active electrode. An electrical current is passed between the active electrode and the return electrode. In alternate embodiments the return electrode is a dispersive pad, and the electrical current is passed directly through a patient""s tissue.
In another exemplary embodiment, the system further comprises a fluid delivery element for supplying electrically conductive fluid to the fissure to substantially surround at least the active electrode with electrically conductive fluid and to locate electrically conductive fluid between the active electrode and the fissure. The fluid delivery element may be located on the probe, e.g., a fluid lumen or tube, or it may be part of a separate instrument. A high frequency voltage source generates a voltage sufficient to seal the fissure. The electrically conducting fluid will preferably generate a current flow path between the active electrode(s) and one or more return electrode(s). In a specific configuration, the return electrode is located on the probe and spaced a sufficient distance from the active electrode(s) to substantially avoid or minimize current shorting therebetween and to shield the return electrode from tissue at the target site.
In another aspect, the present invention may be used to both ablate or shrink a portion of the nucleus pulposus, to reduce the water content of the nucleus pulposus which will reduce the pressure of the nucleus pulposus on the annulus. In one embodiment, the RF energy heats the tissue directly by virtue of the electrical current flow therethrough, and/or indirectly through the exposure of the tissue to fluid heated by RF energy, to elevate the tissue temperature from normal body temperatures (e.g. 37xc2x0 C.) to temperatures in the range of 45xc2x0 C. to 90xc2x0 C., preferably in the range from about 60xc2x0 C. to 70xc2x0 C.
The system and methods of the present invention may optionally include a temperature controller coupled to one or more temperature sensors at or near the distal end of the probe. The controller adjusts the output voltage of the power supply in response to a temperature set point and the measured temperature value. The temperature sensor may be, for example, a thermocouple, located in the insulating support that measures a temperature at the distal end of the probe. In this embodiment, the temperature set point will preferably be one that corresponds to a tissue temperature that results, for example, in the contraction of the collagen tissue, i.e., about 60xc2x0 C. to 70xc2x0 C. Alternatively, the temperature sensor may directly measure the tissue temperature (e.g., infrared sensor).